1. Field of the Invention
The present invention relates to a method of compensating for a bias for efficient servo control of a hard disk drive, and, more particularly, to a bias compensation method of optimally compensating for a bias force with respect to elapsed usage time of a hard disk drive, and a bias force profile generation method, recording media, and a hard disk drive which is appropriate to the bias compensation method.
2. Description of the Related Art
Generally, a hard disk drive is an apparatus for magnetically storing data on a rotating magnetic disk. Because of its large capacity and high speed, it is widely used as an auxiliary memory device of a computer system.
In the hard disk drive, data is stored in tracks formed as concentric circles on a magnetic disk. These tracks are accessed by a magnetic head that reads data from and writes data to the magnetic disk. Moving the magnetic head over the magnetic disk to one of the tracks is referred to as track seek.
A disturbance acting on the magnetic head during the track seek of the hard disk drive is referred to as a bias. In an HDD, major factors which affect the bias force include a pressure difference occurring when an air flow generated by the rotation of the disk pushes sides of the head, a tension of a flexible cable connected to the head, the characteristics of a bearing axis of a voice coil motor, etc. Accordingly, this bias force varies with respect to the position, the movement distance and the movement direction of the magnetic head. More specifically, the initial driving power of the voice coil varies with respect to the position and movement direction of the magnetic head and the initial movement speed of the magnetic head varies with respect to the movement distance in a seek operation. Accordingly, bias should be compensated with respect to the position, the movement distance, and the movement direction of the magnetic head. This bias force compensation method is disclosed in Japanese Patent Application Laid-Open Nos. Hei 6-215508, Hei 4-339371, and Hei 6-20408, etc.
According to the conventional bias force compensation method, a surface of a disk is divided into a plurality of areas ranging from its inner circumference to its outer circumference, and the bias force in each area is measured and stored in a bias compensation table. Then, the bias compensation table is referred to for bias compensation on a track seek operation.
However, a bias force can vary with respect to user environments. Accordingly, in actual practice, it is widely adopted that if the difference between the measured bias force according to the positions of the head and the bias force of the corresponding head position stored in the bias force table is considerably large, then the bias forces in that vicinity of the corresponding head position or in all areas in the bias force table are updated.
However, if only the bias forces in that vicinity are updated, since the remaining areas keep the previous bias forces without change, a deviation between bias forces in adjacent areas becomes larger.
Meanwhile, if the bias forces of all areas are updated, it is difficult to calculate a new adequate bias force for each area, and the calculation takes [too] much time. Further, assuming that the bias forces change non-linearly, because it needs to adapt a proportional constant with respect to the position of the head on the disk, the calculation takes quite a lot of time.